INFLUENCE OF THE CONCENTRATION OF A LOW-MOLECULAR ORGANIC SOLUTE ON THE FLUX REDUCTION OF A POLYETHERSULFONE ULTRAFILTRATION MEMBRANE

Drastic flux reductions are sometimes encountered during ultrafiltrati on of solutes much smaller than the membrane pores. This usually occur s during ultrafiltration of hydrophobic, low-molecular solutes, such a s fatty acids, alcohols and alkanes. The influence of the concentratio n of a carboxylic acid, octanoic acid, on the flux of a polyethersulph one membrane was studied in this investigation. The concentration was found to have a marked influence on the flux. The flux reduction was m oderate at low concentrations, but became severe above a certain, crit ical concentration. Two fur-reducing mechanisms were evaluated; reduct ion of the effective pore radius by adsorption of solute molecules on the pore walls, and blocking of pores by capillary condensation. The a dsorption of octanoic acid on a hydrophobic solid surface was studied by null ellipsometry.